The invention relates to the sidewalls and the beads of tires and, more particularly, the cushion compounds in contact with the reinforcing cords of the carcass or carcasses anchored in the beads.
The beads of tires are rigid parts which function to seat the tire on the rim and anchor the carcasses. Their contact with the rim, particularly the rim flanges, must be made, during travel, with a minimum of slippage to reduce wear due to rubbing against the rim. The sidewalls, on the other hand, are very flexible. It is important to avoid any sudden variation in rigidity between the beads and the sidewalls, particularly to ensure good endurance of the tires. Thus the beads may be considered to comprise two parts, an anchoring zone whose walls are designed to come into contact with the seat and the flange of the rim and, radially outwardly, a transition zone adjacent to the sidewalls. The anchoring means of the carcasses are arranged in the anchoring zone of the bead.
European Patent 0,582,196 discloses a tire comprising a tread extended by two sidewalls and two beads, as well as a carcass anchored in the two beads and having an annular reinforcement. The carcass is made up of cords arranged in adjacent fashion, aligned circumferentially and in contact with at least one layer of cushion compound having a very high modulus of elasticity in the anchoring zone of the bead that contains the annular reinforcement. In this tire, the annular reinforcement of the anchoring zone of the bead is made up of piles of circumferential cords with a layer of cushion compound of high modules or elasticity interposed between the reinforcing cords of the carcass and said piles.
The mode of anchoring of the carcass of this tire has the advantage of avoiding a sudden variation in rigidity due to the turn-up end of the carcass. The change in rigidity between the anchoring zone of the carcass and the sidewalls can thus be much more gradual.